How we cite our quotes:
Even in Gwendolen's mind that result was one of two likelihoods that presented themselves alternately, one of two decisions towards which she was being precipitated, as if they were two sides of a boundary-line, and she did not know on which she should fall. (13.53)
To marry Grandcourt or not to marry Grandcourt? That is the question.
The prospect of marrying Grandcourt really seemed more attractive to her than she had believed beforehand that any marriage could be: the dignities, the luxuries, the power of doing a great deal of what she liked to do, which had now come close to her, and within her choice to secure or to lose, took hold of her nature as if it had been the strong odour of what she had only imagined and longed for before. (13.53)
Gwendolen has a lot of ambitions to be in control not only of herself, but also of others. She's not totally into the idea of marrying Grandcourt, but she knows she has a choice to make: between getting everything she wants in terms of material possessions and financial security, or not marrying him.
"Do be serious with me for a moment, dear. Am I to understand that you mean to accept him?"
"Oh pray, mamma, leave me to myself," said Gwendolen, with a pettish distress in her voice. (13.75-76)
Haven't we all been in this situation – you think you know what you want, and then you second-guess your choice? Gwendolen thought she wasn't going to accept Grandcourt, but now she's not so sure.